题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064456-93652.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064456-49090.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064457-90251.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064456-93652.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064457-90251.png)
A.![]() | B.![]() | C.![]() | D.![]() |
答案
解析
试题分析:首先由图可得f(4)的值,进而逐一给出f(3),f(4),…,的值,分析可得从n-1条直线增加为n条直线时,交点的数目会增加n-1,即f(n)=f(n-1)+n-1,然后利用数列求和的办法计算可得答案. 解:如图,4条直线有5个交点,故f(4)=5,由f(3)=2,=f(4)=f(3)+3,…分析可得,从n-1条直线增加为n条直线时,交点的数目会增加n-1, f(n)=f(n-1)+n-1,累加可得f(n)=2+3+…+(n-2)+(n-1)=
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064457-42599.png)
故选A.
点评: 本题考查归纳推理的运用,注意运用数列的性质来发现其中的规律,并进行计算
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064450-67770.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064450-58998.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064451-31389.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064451-20682.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064451-85783.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064451-58203.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064452-96797.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064452-41170.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064452-40704.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064450-58998.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064451-31389.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064452-66660.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064452-74937.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064451-20682.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064446-48740.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064447-67983.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064447-82619.png)
(1)所以
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064447-65055.png)
(2)所以
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064447-82619.png)
(3)假设
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064447-72365.png)
(4)那么,由
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064447-67983.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064448-58851.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064448-66761.png)
这四个步骤正确的顺序应是
A.(1)(2)(3)(4) | B.(3)(4)(2)(1) | C.(3)(4)(1)(2) | D.(3)(4)(2)(1) |
0 3 → 4 7 → 8 11 …
↓ ↑ ↓ ↑ ↓ ↑
1 → 2 5 → 6 9 → 10
根据规律,从2 009到2 011的箭头方向依次为________.
①↓→ ②→↑ ③↑→ ④→↓
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064436-92518.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064436-34936.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064436-28749.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064437-92219.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064437-18144.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064437-33569.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064437-69260.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064437-61674.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064438-32940.png)
根据上述分解规律,则
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064438-59532.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064438-89384.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064436-34936.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064431-31566.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191106/20191106064431-31566.png)
A.大前提错误 | B.小前提错误 | C.推理形式错误 | D.以上都不是 |
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